1. Field of the Invention
The present invention relates to a lighting device. In particular, the present invention relates to a lighting device using semiconductor light-emitting element such as laser beam source, and to a projection type display apparatus using the lighting device.
2. Description of the Related Art
Recently, the projection- (projector-) type display apparatus has come into wide use. However, with the development of high image quality resulting from high-vision, high-level color rendering is required as the image display apparatus. Short arc type discharge lamps such as mercury lamps, metal halide lamps and xenon lamps are mainly used as the light source for the projection type display apparatus.
In such discharge lamps, a reflecting mirror guides an optical path, and unnecessary light is removed using individual filters. A fly-eye lens divides irradiating light, and overlaps and averages it together with a condenser lens, such that the discharge lamp irradiates a light valve with approximately uniform quality. Thereafter, the irradiating light guided by a dichroic mirror is transmitted by the light valve, and synthesized as projection light by complex prism so that image can be displayed on a screen.
However, the above-noted light source is a continuous spectrum light source having a steep peak. For this reason, in many projection type display devices, it is difficult to provide color rendering, that is, provide both monochromatic RGB purity and the total luminance flux after optical synthesis. In order to give priority to color rendering, only a slight region, equivalent to RGB wavelength, in the emission spectrum of the discharge lamp should be used as effective light. As a result, the total output luminance flux after synthesis becomes small.
On the other hand, in order to give priority to output luminance flux value, RGB selection light should be expanded to the maximum range having no intersection. As a result, not only the chromatic purity of each color deteriorates, but also chromatic phenomenon is confirmed in white uniformity after synthesis; therefore, color rendering is lost. The removed unnecessary light has the possibility of causing the problem as heating or stray light.
The above problem results from the discharge lamp having continuous and steep spectrum distribution. A projection type display device using semiconductor light sources such as light emitting diodes and laser diodes, have been developed as a new source for solving the above problem. For example, Jpn. Pat. Appln. KOKAI Publication No. 2000-305040 discloses a technique in which a light emitting diode is arranged before a complex prism of the projection type display apparatus, so that color rendering and white balance can be improved. By doing so, red color component, which has not been sufficiently obtained by only discharge lamp, is replenished, so that color rendering can be improved.
However, in general, light is easily diffused in the light emitting diode. For this reason, the conventional lighting device has the following problem that luminance and efficiency are not sufficiently improved in the projection light, which is the final output.